Battery cell including electrolyte ion concentration measurement unit and method for measuring electrolyte concentration using same

ABSTRACT

The present invention relates to a battery cell including an electrolyte ion concentration measurement unit and a method for measuring an electrolyte concentration using same. The battery cell according to the present invention comprises a measurement unit in which a first electrode plate, an insulation film, and a second electrode plate are sequentially stacked on one another, wherein the measurement unit is inserted between a separator of the battery cell and an electrode thereof, and thus can directly measure an electrolyte concentration between the separator and the electrode. Therefore, the battery cell can be simply manufactured and has excellent stability. In addition, according to the present invention, the method for measuring an electrolyte concentration of a secondary battery using the battery cell enables measurement of electrolyte concentration in real time even during the use of the battery and can measure an electrolyte concentration of the separator more accurately and quickly than a conventional technology.

TECHNICAL FIELD

The present invention relates to a battery cell including an electrolyteion concentration measuring unit and a method for measuring electrolyteconcentration using the same.

This application claims the benefit of priority based on Korean PatentApplication No. 10-2018-0131467, filed on Oct. 31, 2018, and the entirecontents of the Korean patent application are incorporated herein byreference.

BACKGROUND ART

As the price of energy sources increases due to depletion of fossilfuels and the interest in environmental pollution increases, the demandfor environmentally friendly alternative energy sources becomes anindispensable factor for future life. Especially, as technologydevelopment and demand for mobile devices are increasing, demand forsecondary batteries as energy sources is rapidly increasing.

Typically, in terms of the shape of the battery, there is a high demandfor a prismatic secondary battery and a pouch-type secondary batterythat can be applied to products such as mobile phones with a smallthickness. In terms of materials, there is a high demand for lithiumsecondary batteries such as lithium ion batteries and lithium ionpolymer batteries having high energy density, discharge voltage, andoutput stability.

Generally, in order to prepare a secondary battery, first, a positiveelectrode and a negative electrode are formed by applying an electrodemixture containing an electrode active material to a surface of acurrent collector, then a separate is interposed therebetween to therebymake an electrode assembly, which is then mounted in a cylindrical orrectangular metal can or inside a pouch-type case of an aluminumlaminate sheet, and a liquid electrolyte is injected or impregnated intothe electrode assembly or a solid electrolyte to prepare a secondarybattery.

The liquid electrolyte in which the solvent is a liquid in theelectrolyte (hereinafter referred to as an “electrolyte”) is alsocommonly referred to as an electrolyte. A nonaqueous electrolyte isgenerally used as the electrolyte for the lithium secondary battery andis composed of an organic solvent and a salt of an organic or inorganiccompound such as LiClO₄, LiBF₄, LiPF₆, LiAsF₆, LiCF₃SO₃, LiN(CF₃SO₂)₃,etc.

The electrolyte for the lithium secondary battery serves to transportlithium ions as a medium for transferring ions of the battery.Therefore, in order to obtain excellent battery performance, it isimportant to select an electrochemically stable electrolyte having highion conductivity between both electrodes.

The ion conductivity may be expressed as a sum of cations and anions.Since only lithium cations contribute to the ion conductivity byperforming the electrochemical reaction in the lithium secondarybattery, the fraction of the cations among all the ions, that is, thecation yield is important. On the other hand, the cation yield generallydepends on the concentration of salt, temperature, radius of ions andcharge amount in the electrolyte, and is known to be greatly affected bythe concentration and temperature of the salt.

However, the electrolyte ion concentration (hereinafter referred to as“electrolyte concentration”) of the lithium secondary battery maydecrease as the battery deteriorates due to repeated charge/dischargecycles and/or side reactions of the battery. Accordingly, when the ionconductivity is lowered, the lithium ions entering and leaving the twoelectrodes are not properly transported during charging and discharging,and thus the capacity of the electrode active material cannot besufficiently realized.

Therefore, it is possible to check the charge/discharge cycle or thebattery deterioration state by measuring the electrolyte concentrationchange, and the electrolyte concentration change value becomes anelectrochemical indicator that can measure the overall performance ofthe secondary battery.

In this regard, conventionally, a method of measuring the concentrationof an electrolyte was used. According to the method, after immersing arod-shaped conductive metal rod in an electrolyte, the resistance valuebetween the wires attached to the rod is calculated, and the electrolyteconcentration is estimated by using the temperature data measured by aseparate temperature sensor. However, in this method, it was notpossible to directly measure the concentration of electrolyte betweenthe electrode and the separator of the battery cell where the lithiumions were transferred due to the size of the conductive metal rod. Onlyan approximate prediction was possible by an indirect method ofimmersion in the electrolyte outside the battery cell. In addition,there was a problem in that the change in the electrolyte concentrationof the battery could not be measured in real time.

As another method for measuring electrolyte concentration, KoreanLaid-Open Patent Publication No. 10-2010-0098453 discloses a lithium ionsecondary battery capable of measuring the concentration of lithium ionsin an electrolyte at a predetermined site, an assembled battery usingthe lithium ion secondary battery, a vehicle having the assembledbattery and a battery-mounting device, a battery system which canacquire concentration correlation physical quantity in a lithium ionsecondary battery, and a method of detecting deterioration of thelithium ion secondary battery. The patent document discloses a method ofmeasuring an electrolyte concentration by interposing a first electrodebody portion and a second electrode body portion in a state spaced apartbetween a separator and an electrode, respectively, as an embodiment.This is a method of reducing the size of a conventional conductive metalbar measuring device and manufacturing it in the form of a thin film,and inserting it into a space between the separator and the electrode tothereby measure the concentration of the electrolyte therebetween. Thismethod has an advantage over the conventional method in which it wasdifficult to directly measure the electrolyte concentration between theelectrode and the separator. However, the measuring method of the patentdocument is to proceed by inserting the two measuring devices indifferent positions, respectively. When the inserted measuring devicesare in contact with each other to thereby generate a short circuit, notonly it is impossible to measure, but it can also cause fever and fire.Therefore, each of the measuring devices should be inserted to be spacedapart by a predetermined interval or more, and there is a constraintthat the spaced state should be maintained. In addition, since aseparate process of attaching a separate insulating film to theseparator is required, the manufacturing method is difficult, and thusthere is a limitation in the insertion position and the size of themeasuring device. In addition, even if inserted into the battery cell ofthe measuring device in this way, if the position of the measuringdevice is changed by an external impact, there is still a risk of heatgeneration and ignition due to a short circuit, as described above, andthus it may cause a problem of low stability.

DISCLOSURE Technical Problem

The present invention provides a battery cell including a measuring unitfor measuring the electrolyte concentration in measuring the electrolyteconcentration of the lithium secondary battery, and a method ofmeasuring the electrolyte concentration using the same.

In this regard, the object of the present invention is to provide abattery cell for measuring secondary battery electrolyte concentration,which is capable of directly measuring electrolyte concentration andperforming real-time measurement while using a secondary battery, and iseasily manufactured and has a high stability, and a method for measuringelectrolyte concentration using the same.

Technical Solution

In order to solve the above problems, a battery cell of the presentinvention includes a measuring unit in which a first electrode plate, aninsulating film and a second electrode plate are sequentially stacked.

The measuring unit may be inserted between a separator and an electrodeof the battery cell to thereby measure the electrolyte concentration ofthe battery cell.

Further, wires drawn to an outside of the battery cell may be connectedto the first electrode plate and the second electrode plate,respectively, and the wires may be drawn out the external side of thebattery cell to thereby be connected to the resistance measuring deviceoutside the battery cell.

In an embodiment of the present invention, one or more through-holes maybe formed on the first electrode plate or the second electrode plate.The measuring unit of the present invention is used to measure theconcentration after impregnating the electrolyte in the insulating filminterposed between the first electrode plate and the second electrodeplate, and when the through-hole is formed on the first electrode plateand the second electrode plate, the electrolyte may be quickly permeatedinto the measuring unit through the through-hole and be absorbed in theinsulating film.

In an embodiment of the present invention, in order to increase theelectrolyte impregnation speed, the shapes and/or sizes of through-holesformed on the first electrode plate and the second electrode plate maybe set to be the same. In such a case, respective through-holes formedon the first electrode plate and the second electrode plate may bepositioned to correspond to each other, and the insulating filmimpregnation speed of the measuring unit may be more improved.

At this time, a horizontal cross-sectional area of each through-hole maycorrespond to 0.1 to 45%, more preferably 1 to 10% of a horizontalcross-sectional area of the first electrode plate or the secondelectrode plate before the through-hole is formed.

Further, as the through-holes are formed on the first electrode plateand the second electrode plate, the porosity of the first electrodeplate and the second electrode plate may be 30 to 45%, more preferably34 to 42%.

Further, the thickness of the measuring unit may be 25 to 35 μm, morepreferably 28 to 30 μm.

In an embodiment of the present invention, when the measuring unit isinserted into the battery cell, the first electrode plate or the secondelectrode plate may be in contact with the electrode of the batterycell, depending on the inserted portion. In such a case, the insulatingfilm may be further included on the outer surface of the first electrodeplate or the second electrode.

In an embodiment of the present invention, the first electrode plate andthe second electrode plate may be made of one metal selected from thegroup consisting of aluminum, copper, and nickel or an alloy of two ormore kinds thereof, and more preferably be made of aluminum or copper.

In an embodiment of the present invention, the insulating filminterposed in the measuring unit may be a porous film of apolyolefin-based polymer material, and the same material as that of theseparator of the battery cell may be used.

Meanwhile, the present invention provides a method of measuringelectrolyte concentration of a secondary battery by using a battery cellincluding a measuring unit.

Specifically, a method of measuring electrolyte concentration of asecondary battery according to an embodiment of the present inventionmay include:

manufacturing a measuring unit in which a first electrode plate, aninsulating film and a second electrode plate are sequentially stacked(s1);

connecting an electric wire to one end of the first electrode plate andthe second electrode plate (s2);

inserting the measuring unit into a space between the electrode of thebattery cell and the separator (s3); and

drawing out the electric wire to the outside of the battery cell (s4);and

calculating a concentration of electrolyte ions contained in a polymerfilm by connecting a measuring device to the electric wire (s5).

The electrolyte ion concentration in the step s5 may be calculated bymeasuring a resistance value between the first electrode plate and thesecond electrode plate after applying current to the wire and then usinga temperature of the electrolyte which is measured by using a separatetemperature sen_sor.

In the step s1 of manufacturing the measuring unit, one or morethrough-holes may be formed on the first electrode plate and the secondelectrode plate in order to improve the electrolyte impregnation speed.

At this time, a horizontal cross-sectional area of each through-hole maycorrespond to 0.1 to 45%, more preferably 1 to 10% of a horizontalcross-sectional area of the first electrode plate or the secondelectrode plate before the through-hole is formed. Further, as thethrough-holes are formed on the first electrode plate and the secondelectrode plate, the porosity of the first electrode plate and thesecond electrode plate may be 30 to 45%, more preferably 34 to 42%.Further, the thickness of the measuring unit may be 25 to 35 μm, morepreferably 28 to 30 μm.

Advantageous Effects

The battery cell according to the present invention includes a measuringunit in which the first electrode plate, the insulating film and thesecond electrode plate are sequentially stacked. The measuring unit isinserted between the separator and the electrode of the battery cell, soit is possible to directly measure the concentration of the electrolytebetween the separator and the electrode, and the manufacturing is simpleand stability is high.

In addition, according to the secondary battery electrolyteconcentration measurement method of the present invention using thebattery cell, the electrolyte concentration can be measured in real timeeven during the use of the battery, and it is possible to measure theelectrolyte concentration of the separator more accurately and quicklythan in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a battery cell structure including an electrolyteconcentration measuring unit according to an embodiment of the presentinvention.

FIG. 2 shows an electrolyte concentration measuring unit and the wireconnected to the measuring unit according to an embodiment of thepresent invention.

FIG. 3 illustrates a structure of an electrolyte concentration measuringunit according to an embodiment of the present invention.

FIG. 4 shows a side cross-sectional view of the electrolyteconcentration measuring unit according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The terms and words used in the present specification and claims shouldnot be construed as limited to ordinary or dictionary terms and theinventor may properly define the concept of the terms in order to bestdescribe its invention. The terms and words should be construed asmeaning and concept consistent with the technical idea of the presentinvention. Accordingly, the embodiments described in the specificationand the configurations described in the drawings are only the mostpreferred embodiments of the present invention, and do not represent allof the technical ideas of the present invention. It is to be understoodthat there may be various equivalents and variations in place of them atthe time of filing the present application.

In the present specification, when a part is “connected” to anotherpart, this includes not only “directly connected” but also “electricallyconnected” between the parts while having another element therebetween.

Also, throughout the specification, when an element is referred to as“including” an element, it is understood that the element may includeother elements as well unless specifically stated otherwise.

As used throughout this specification, the terms “about”,“substantially”, and the like, are used to mean a value or somethinglike this when unique manufacturing and material tolerances arepresented, and the terms are used to prevent unscrupulous infringersfrom unfair use of the disclosure including accurate or absolute figuresin order to aid in the understanding of the present disclosure.

Throughout this specification, the term “combination(s) thereof”included in the expression of the Markush form means one or moremixtures or combinations selected from the group consisting of theelements described in the Markush form representation, and it means toinclude one or more selected from the group consisting of the abovecomponents.

Throughout this specification, the expression “A and/or B” means “A or Bor both.”

Hereinafter, the present invention will be described in detail.

The present invention provides a battery cell for measuring the ionconcentration of the electrolyte and a measuring method using the same.

The conventional method of measuring electrolyte concentration using twoconductive metal rods has problems that accuracy is low, and electrolyteconcentration cannot be measured in real time while using secondarybatteries.

In this regard, Korean Patent Laid-Open Publication No. 10-2010-0098453discloses a technology of manufacturing a conventional measuring device,which is in the form of a rod, in the form of a small thin film andinserting it between an electrode and a separator. However, themanufacturing of the measuring device is difficult and limited, and itdoes not solve the problem that heat and ignition may occur when a shortcircuit occurs due to an external shock.

The present invention further improves the conventional secondarybattery electrolyte concentration measurement method, and since thedistance between the first electrode plate and the second electrodeplate of the measuring unit is very small, the magnitude of theresistance value is very small, thereby minimizing the effect ofresistance, which is one of the electrolyte concentration measurementvariables. As such, the change in electrolyte concentration can bemeasured more precisely and in real time, compared to Korean PatentPublication No. 10-2010-0098453. That is, the size of the resistancevalue is small and the sensitivity according to the change of theelectrolyte concentration is increased, so that the resolution of themeasurement is further increased, thereby enabling accurateconcentration change measurement.

In addition, when comparing the present application with the prior artKorea Patent Publication No. 10-2010-0098453, the prior art disclosesthat each electrode plate is attached to the separator to measure theelectrolyte concentration, and an additional insulating film is attachedthereon to prevent the short circuit. Therefore, the method requires acomplicated and difficult additional process that is different from theconventional battery cell manufacturing process, and is not suitable formass production, and thus the industrial availability is not high.

On the contrary, the measuring unit according to the present inventioncan be easily manufactured using a conventional electrode laminationdevice, and insertion is also very simple. In order to performinsertion, a stacking process is to be temporarily stopped at thedesired position during the stacking process of the battery cell, andthen the measuring unit is placed in the battery cell and the stackingprocess is resumed.

In the aspect of effects, the measuring unit of the present inventionminimizes the interference of the outside by minimizing the size of themeasuring unit by stacking the electrode plates at the time ofmeasurement, and furthermore, it has a minimal effect on the external,that is, the electrode of the battery. In contrast, in the prior art,since two electrode plates are separated and inserted separately, thearea occupied by foreign matters between the separators increases, whichmay cause an increase in resistance during charge and discharge.

In addition, in the case of using a method of attaching to the batteryseparator of the prior art, since the two current collectors may beshort-circuited by being connected to the positive electrode and thenegative electrode of the battery, there is a problem that themeasurement method may become also difficult. For example, an additionaldevice or process may become necessary for the measurement.

On the other hand, since the measuring unit of the present invention canbe easily inserted during the battery cell stacking process aftermanufacturing and testing in advance as described above, processabilityis excellent and calibration through pre-test is also possible. That is,the measuring unit according to the present invention is not only easyto manufacture in a simple process, but also easy to install because itis only inserted between the separator and the electrode in a typicalbattery cell manufacturing process, and precise measurement is possibleeven without a demanding additional process.

Hereinafter, a battery cell and a method for manufacturing the sameaccording to the present invention, and a method for measuringelectrolyte concentration using the battery cell according to thepresent invention will be described in detail.

The present invention provides a battery cell in which the electrode andthe separator are sequentially stacked and is characterized in that, byincluding a measuring unit for measuring the concentration of theelectrolyte therein, the electrolyte concentration between the electrodeand the separator can be accurately measured. In addition, in thepresent invention, the measuring unit is inserted between the electrodeand the separator, and the wire drawn out of the battery cell and thecompleted secondary battery is connected to the measuring unit, therebyallowing the electrolyte concentration to be measured in real time evenduring use of the battery.

According to a specific embodiment of the present invention, theelectrode assembly includes an electrode laminate in which twoelectrodes having opposite polarities are alternately stacked byinterposing a separator therebetween. The electrode may be a negativeelectrode or a positive electrode, and the separator may be interposedbetween the positive electrode and the negative electrode to therebyelectrically insulate them.

The positive electrode may include, for example, a positive electrodecurrent collector made of aluminum (Al) and a positive electrode activematerial layer formed by coating a positive electrode active material onone or both surfaces of the positive electrode current collector.Similarly, the negative electrode may include a current collector madeof copper and a negative electrode active material layer formed bycoating a negative electrode active material on one surface of thecurrent collector.

Layered positive electrode active material such as LiCoO₂, LiNiO₂,LiNi_(1-y)Co_(y)O₂(0<y<1), LiMO₂(M=Mn, Fe, etc.),Li(Ni_(a)Co_(b)Mn_(c))O₂(0<a<1, 0<b<1, 0<c<1, a+b+c=1),LiNi_(1-y)Mn_(y)O₂(0≤y<1); spinel type positive electrode activematerial such as LiMn₂O₄, LiMn_(2-z)Co_(z)O₄(0<z<2),LiMn_(2-z)Ni_(z)O₄(0<z<2), Li(Ni_(a)Co_(b)Mn_(c))O4(0<a<2, 0<b<2, 0<c<2,a+b+c=2); olivin type positive electrode active material such as LiCoPO₄and LiFePO₄, etc. may be used as the positive electrode active material.

Carbonaceous material such as petroleum coke, activated carbon,graphite, non-graphitized carbon, graphite carbon; metal complex oxideof LixFe₂O₃(0≤x≤1), Li_(x)WO₂ (0≤x≤1), Sn_(x)Me_(1-x)Me′_(y)O_(z) (Me:Mn, Fe, Pb, Ge; Me′: Al, B, P, Si, group 1, 2, and 3 elements of theperiodic table, halogen; 0<x≤1; 1≤y≤3; 1≤z≤8); lithium metal; lithiumalloy; silicon-based alloy; tin alloy; oxide such as SnO, SnO₂, PbO,PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄, Bi₂O₅;conductive polymer such as polyacetylene; Li—Co—Ni-based material, etc.

In the present invention, the electrode tab of the negative electrodetab or positive electrode tab may be formed for the negative electrodeand the positive electrode, respectively. The electrode tab may beformed integrally with the negative electrode current collector and/orthe positive electrode current collector, for example, and correspondsto a non-coated region where the electrode active material is notcoated. That is, the electrode tab T may be formed by punching a regioncorresponding to a region where the electrode active material is notcoated on the surface of the current collector to be formed into anappropriate shape.

In one specific embodiment of the present invention, the separatorserves as an ion conductive barrier for passing ions while blockingelectrical contact between the negative electrode and the positiveelectrode. According to one specific embodiment of the presentinvention, the separator may include a porous polymer substrate having aplurality of micropores. Furthermore, the separator may have a porouscoating layer including a plurality of inorganic particles and a polymerbinder resin on the surface of the porous polymer substrate. The porouscoating layer is a layer in which inorganic particles are bonded bypoint bonding and/or surface bonding through a binder resin, and thecoating layer has a porous structure due to the interstitial volumebetween the inorganic particles.

The porous polymer substrate may be made of at least one of polymerresins such as polyolefin, polyethylene terephthalate, polybutyleneterephthalate, polyacetal, polyamide, polycarbonate, polyimide,polyetheretherketone, polyethersulfone, polyphenylene oxide,polyphenylene sulfide, and polyethylene naphthalene, but is notparticularly limited thereto. In addition, any of a sheet-like film, inwhich a polymer resin is melted and formed into a film, and a nonwovenfabric, in which filaments obtained by melting and spinning a polymerresin are integrated, may be used as the porous polymer substrate.Preferably it is a porous polymer substrate prepared in the form of asheet by melting/molding the polymer resin.

Referring to FIG. 1 , the battery cell 100 according to an embodiment ofthe present invention may include a measuring unit 130 for measuring theelectrolyte concentration between the positive electrode 121 and theseparator, or between the negative electrode 122 and the separator 110.The measuring unit 130 is characterized in that the wire 140 drawn outof the battery cell 100 is connected.

Referring to FIGS. 2 and 3 , the measuring unit 130 has an insulatingfilm 133 interposed between the first electrode plate 131 and the secondelectrode plate 132, and they are sequentially stacked. On the otherhand, a wire 140 connected to the measuring unit includes a wire 141connected to the first electrode plate 131 and a wire 142 connected tothe second electrode plate 132, respectively, and the wire 140 is drawnout of the battery cell as shown in FIG. 1 .

The measuring unit is inserted between the electrode and the separator110 of the battery cell 100 to measure the concentration of theelectrolyte between the separator and the electrode. According to theexemplary embodiment of FIG. 1 , the measuring unit is illustrated asbeing inserted between the negative electrode 122 and the separator 110,but may be inserted between the positive electrode 121 and the separator110. In this case, the measuring unit does not necessarily need to beinserted between the electrode and the separator of the battery cell,and may be inserted at another position that can be inserted accordingto the size, shape, and structure of the battery cell.

As shown in FIG. 1 , according to an embodiment of the presentinvention, the insulating layer 133 of the measuring unit is interposedbetween the first electrode plate 131 and the second electrode plate 132to absorb the electrolyte between the positive electrode 121 or thenegative electrode 122 of the battery cell and the separator 110, andwhen a current is applied to the wire 140 connected to the firstelectrode plate 131 and the second plate 132, the resistance value maybe measured to calculate the concentration of the electrolyte. On theother hand, the wires are drawn out after assembling the secondarybattery, and it is possible to measure the real-time electrolyteconcentration at any time even while using the battery.

The insulating film 133 may be made of a porous film made of apolyolefin-based polymer material so that the first electrode plate 131and the second electrode plate 132 may be electrically insulated, andthe electrolyte may be easily absorbed and lithium ions may be movedsmoothly. Further, the used material may be the same material used forthe separator. In addition, when a short circuit is expected accordingto the insertion part of the measuring unit, it is also possible toattach an additional insulating film 134 to the outer surface of theelectrode plate that needs to be electrically insulating as shown inFIGS. 3 and 4 .

Meanwhile, the first electrode plate and/or the second electrode platemay have a through-hole having a columnar shape, as shown in oneembodiment of FIGS. 2 to 4 . In this case, as shown in FIG. 3 , when thethrough-holes formed in the first electrode plate and the secondelectrode plate are positioned so that their shape and positioncorrespond to each other in a direction perpendicular to the electrodeplate, the electrolyte on the outside of the measuring unit is moreeasily penetrated inside through the through hole. As a result, theelectrolyte is quickly absorbed into the insulating film, whereby theconcentration change of the electrolyte can be measured more quickly inreal time.

To this end, the through-hole may have a minimum size to easilypenetrate the electrolyte, but if the through-hole is too small, it maybe difficult to form the through-hole by conventional equipment.Therefore, when considering the efficiency of the manufacturing process,each of the through-holes preferably occupies 0.1% or more relative tothe horizontal cross-sectional area of the first electrode plate and/orthe second electrode plate before forming the through-hole.

In addition, one or more through-holes may be formed in the electrodeplate, and the porosity of the electrode plate is determined accordingto the size and number of the through-holes. The porosity of theelectrode plate is a value obtained by dividing the sum of the volumesof all the through-holes formed by the volume of the electrode platebefore forming the through-holes, and the porosity of the electrodeplate is preferably adjusted to a range similar to that of theinsulating film absorbing the electrolyte. Specifically, the porosity ofthe electrode plate is preferably adjusted to have a porosity of 30 to45%, and more preferably adjusted to have a porosity of 34 to 42%.

On the other hand, in order to increase the electrolyte impregnationspeed, it is preferable to form the through-hole in the form of a columnhaving a constant diameter. In this case, the porosity of the electrodeplate may be calculated as a value obtained by dividing the horizontalcross-sectional area of the through-hole by the horizontal cross-sectionof the electrode plate.

Therefore, when only one through-hole is formed, it is preferable thatthe horizontal cross-sectional area of the through-hole does not exceed45% of the electrode plate area. Even if it exceeds 45%, it is difficultto expect further improvement of electrolyte permeability, and if thethrough-hole is formed too large, the rigidity of the electrode platemay be deteriorated, which may cause a defect such as distortion duringpreparing a measuring unit or during inserting the battery cell.

On the other hand, according to the experiments of the presentapplicant, in the case of the electrode plate having the same porosity,the penetration rate is more excellent when a plurality of through-holesare formed than when one through-hole is formed. Therefore, it ispreferable to form two or more through-holes, and when considering theefficiency of the process and the excellent penetration rate, it is mostpreferable to form a plurality of through-holes having a horizontalcross-sectional area of 1 to 10% of the electrode plate area so that theporosity of the electrode plate becomes 30 to 45%.

As described above, when the porosity of the first electrode plateand/or the second electrode plate is preferably set to be 30 to 45%,more preferably 34 to 42% by one or more through-holes formed in thefirst electrode plate and/or the second electrode plate, excellentelectrolyte penetration rate can be expected. However, if the porosityexceeds 45%, it is difficult to obtain uniform quality during themanufacturing process, and the difficulty of manufacturing can increaserapidly by generation of defects, etc., which is not desirable in termsof securing the efficiency of the process, and in such a case, it isdifficult to expect significant improvement in penetration rate. On theother hand, when the porosity is less than 30%, the electrolytepenetration rate is lowered, which is not preferable.

According to an embodiment of the present invention, the thickness ofthe measuring unit of the present invention may be preferably 25 to 35μm, more preferably 28 to 30 μm. The thickness of the measurement unitis preferably as thin as possible because it does not change the shapeof the battery cell even after insertion. However, when the thickness istoo thin below the above range, the mechanical strength of the measuringunit may be lowered, such that the measuring unit may be broken due toexternal impact or the laminated structure may be distorted duringmanufacturing.

On the other hand, when the measuring unit of the present invention isinserted between the electrode and the separator, one outer surface ofthe first electrode plate or the second electrode plate comes in contactwith the electrode. In this case, the insulating layer 134 may befurther provided on an outer surface of the electrode plate which is incontact with the electrode, thereby adding insulation.

The first electrode plate and the second electrode plate may be made ofone metal selected from the group consisting of aluminum, copper, andnickel or an alloy of two or more kinds thereof, and more preferably bemade of aluminum or copper.

The method for measuring the electrolyte concentration using the batterycell including the measuring unit of the present invention may includethe following steps:

-   -   manufacturing a measuring unit in which a first electrode plate,        an insulating film and a second electrode plate are sequentially        stacked (s1);    -   connecting an electric wire to one end of the first electrode        plate and the second electrode plate (s2);    -   inserting the measuring unit into a space between the electrode        of the battery cell and the separator (s3);    -   drawing out the electric wire to the outside of the battery cell        (s4);    -   calculating a concentration of electrolyte ions contained in a        polymer film by connecting a measuring device to the electric        wire (s5).

The concentration of the electrolyte is usually proportional to themagnitude of the electrical conductivity and inversely proportional tothe resistance value. In addition, electrical conductivity is greatlyaffected by temperature. Based on these characteristics, a uniquetemperature curve according to the electrical conductivity andconcentration characteristics appears depending on the type ofelectrolyte.

The electrolyte measurement principle of the present invention uses theabove-described electrolyte concentration characteristic, and in steps5, the resistance value between the first electrode plate and thesecond electrode plate can be measured by applying a current to thewire, from which the approximate concentration of the electrolyte can becalculated. After measuring the temperatures of the electrolyte, andthen the measured temperatures can be amended to an inherent temperaturecurve according to the type of electrolyte, to thereby obtain a preciseelectrolyte concentration measurement results. In this case, atemperature sensor may be separately installed for measuring theelectrolyte temperature.

Meanwhile, in the step s1, through holes may be formed in the firstelectrode plate and/or the second electrode plate to improve electrolytepermeability, and as described above, the porosity of the electrodeplate is determined by the sum of the horizontal cross-sectional areasof the through holes with respect to the horizontal cross-sectional areaof the electrode plate. Hence, the horizontal cross-sectional area ofeach individual through hole is preferably in the range of 0.1 to 45%relative to the total area of the electrode plate prior to through holeformation.

The measuring unit of the present invention is a stack of the firstelectrode plate, the insulating film, and the second electrode plate insequence, and may further include an insulating film on the outersurface of the electrode plate in contact with the electrode of thebattery cell. In this case, the total thickness of the measuring unitmay be preferably 25 to 35 μm, more preferably 28 to 30 μm.

Hereinafter, the manufacturing method of the battery cell including themeasuring unit according to the present invention will be described indetail.

Manufacture of the First Electrode Plate and the Second Electrode Plate

First, a metal foil to be used as the first electrode plate and thesecond electrode plate is cut. Since the first electrode plate and thesecond electrode plate correspond to the size of the measuring unit,first, the type and the insertion site of the battery cell into whichthe measuring unit is to be inserted may be determined, and then may beappropriately adjusted and cut to an appropriate size for easyinsertion. In this case, copper may be used as the metal foil material,but other metals such as aluminum and nickel may be used.

Next, a through hole is formed in the cut metal foil. The through holecan be adjusted in size in consideration of electrolyte penetration rateand stability of the electrode plate, and the shape of the through holemay be preferably in the form of a square column, but if the diameter isuniform, it may be manufactured in another column shape such as acylinder or a triangular column.

Preparation of Insulating Film

The insulating film used in the measuring unit may be manufactured bycutting the porous polymer material into sizes corresponding to thefirst electrode plate and the second electrode plate, and the samematerial as that used for the separator of the battery cell may also beused. At this time, the binder is applied to both surfaces of theinsulating film to a thickness of 3 to 5 μm so that each of the firstelectrode plate and the second electrode plate can be attached to theinsulating film. At this time, if the thickness of the binder is toothin outside the above range, the stability of the measuring unit may belowered. If the binder is too thick, the thickness of the wholemeasuring unit may be thickened. As such, when the binder is insertedinto a battery cell the shape of the battery cell may be deformed.

Manufacture of Measuring Unit

The first electrode plate and the second electrode plate are positionedon one surface and the other surface of the insulating film,respectively. At this time, when the through-holes formed in the firstelectrode plate and the second electrode plate are positioned tocorrespond to each other in the vertical direction perpendicular to theelectrode plate, the electrolyte penetration rate is improved, so thatthe concentration changes in real time can be measured more quickly.

As described above, after forming a laminate such as a sandwich in theorder of the first electrode plate, the insulating film, and the secondelectrode plate, a pressing step is performed. At this time, since thelaminate is torn or distorted due to pressure, it is preferable to carryout the pressing process after wrapping the laminate with a film thatprotects the surface of the laminate, preferably a PET film. At thistime, the pressurizing process of applying pressure to the laminate isthe same as the lamination process of conventional batterymanufacturing. Thereafter, the film surrounding the surface of thepressed laminate is separated to prepare a measuring unit according tothe present invention.

On the other hand, since a short circuit may occur when the electrodeplate of the measuring unit contacts the electrode or the like,depending on the insertion part of the battery cell, an insulating filmmay be additionally attached to the outer side of the electrode plate toprevent the short circuit.

Wire Connection

Wires made of copper and/or other conductive materials are connected tothe first and second electrode plates, respectively. The wire isinserted into the battery cell while being connected to the measuringunit, and depending on the insertion site, the wire may cause a shortcircuit in the battery cell. Therefore, when it is necessary to giveinsulation to the wire, it can be coated with an insulating material.The wire is drawn out and connected to a measuring device for measuringthe resistance of the electrolyte.

Manufacture of Battery Cell and Insertion of Measuring Unit

Production of the battery cell may be performed in the same manner as aconventional manufacturing process. However, when the measuring unitaccording to the present invention is inserted into the battery cell, itis preferable that the battery cell is made during the stacking step ofthe battery cell manufacturing process. When the insertion position ofthe measuring unit is determined, the stacking process can betemporarily suspended, the measuring unit can be placed at a desiredposition, and then the insertion can be simply performed by resuming thestacking process to cover the measuring unit.

Drawing Out and Sealing of Electric Wire

The measuring unit is positioned between the separator and the electrodeof the battery cell, and then the wire is drawn out to the outside.After drawing the wire to the outside, it is possible to seal byattaching the polymer film on the area opened by the insertion of themeasuring unit and applying heat to the area, thereby maintaining asealed state so that outside air does not flow into the inside.

Meanwhile, with respect to battery elements, for example, binders, whichare not described in detail herein, reference may be made to elementscommonly used in the battery field, particularly in the lithiumsecondary battery field.

Hereinafter, the present invention will be described in detail withreference to examples. However, the embodiments according to the presentinvention may be modified into various other forms, and the scope of thepresent invention should not be construed as being limited to theexamples described below. The examples of the present invention areprovided to more fully describe the present invention to those skilledin the art.

EXAMPLE 1

Preparation of the First Electrode Plate and the Second Electrode Plate

A first electrode plate and a second electrode plate having a squareshape of 30 mm in width and 30 mm in length were prepared. Both thefirst electrode plate and the second electrode plate were used bycutting a foil of copper material having a thickness of 6 μm.

Nine identical through holes were formed in the shape of square columnsat equal intervals using a pressure punching equipment on the firstelectrode plate and the second electrode plate. The horizontalcross-sectional area of each of the individual through holes is a squareshape of 6 mm in width and 6 mm in length, and each of the through holesis spaced apart from each other by 4 mm in the horizontal and verticaldirections.

Preparation of Insulating Film

The insulating film has a square shape of 35 mm in width and 35 mm inlength, and a porous polyethylene material having a porosity of 41% wasused. The thickness of the insulating film was 9 μm, and a binder wascoated on both surfaces of the insulating film to form a binder layerhaving a thickness of 4 μm, respectively.

Manufacture of Measuring Unit

A laminate was formed by adjusting the positions such that thethrough-holes formed in the first electrode plate and the secondelectrode plate correspond to each other in a direction perpendicular tothe electrode plate while the insulating film is laminated so as to beinterposed between the first electrode plate and the second electrodeplate.

After wrapping the laminate with a PET film, it was pressurized using anelectrode lamination device, and a wire of copper material was connectedto the first electrode plate and the second electrode plate,respectively, to thereby prepare a measuring unit according to thepresent invention. The thickness of the prepared measuring unit was 29μm, and the porosity of each electrode plate was 36% (horizontal crosssection area of the through hole (6 mm*6 mm)*9/horizontal cross sectionarea of the electrode plate (30 mm*30 mm)).

EXAMPLE 2

The measuring unit was manufactured in the same manner as in Example 1except that nine equal through holes are generated in the first andsecond electrode plates so that the horizontal cross-section of eachindividual through hole becomes a square shape of 2 mm in width and 2 mmin length, and each through hole is spaced 8 mm apart in the transverseand longitudinal directions. The thickness of the prepared measuringunit was 29 μm, and the porosity of the electrode plate was 4%.

EXAMPLE 3

The measuring unit was manufactured in the same manner as in Example 1except that a single through hole was created at the center of the firstelectrode plate and the second electrode plate so that the horizontalcross-section of each individual through hole became a square shapehaving a width of 18 mm and a length of 18 mm. The thickness of theprepared measuring unit was 29 μm, and the porosity of each electrodeplate was 36%.

COMPARATIVE EXAMPLE 1

A measuring unit was manufactured in the same manner as in Example 1,except that neither the first electrode plate nor the second electrodeplate formed a through hole. The thickness of the prepared measuringunit was 29 μm, and the porosity of each electrode plate was 0%.

The difference of the measuring unit manufactured by each said Exampleand the comparative example is shown in Table 1 below.

TABLE 1 No. of Whether through- Through hole through Division hole isformed size holes Porosity Example 1 ◯ width, 9 36% length 6 mm Example2 ◯ width, 9  4% length 2 mm Example 3 ◯ width, 1 36% length 18 mmComparative X — 0  0% Example 1

EXPERIMENTAL EXAMPLE 1 Measurement of Easiness of ElectrolytePenetration

In order to compare the electrolyte impregnation performance of themeasuring unit manufactured by each of the above Examples andComparative Examples, a comparative experiment about the ease ofpenetration of the electrolyte was carried out.

First, the measuring unit according to the above Examples andComparative Examples is prepared and sufficiently dried at roomtemperature, and then resistance measurement was started by connecting aresistance measuring device to the wire connected to the measuring unit.

Thereafter, the measuring unit was impregnated in an electrolyte havingan ion concentration of 0.5 M which is prepared by dissolving LiPF₆ in aco-solvent which is generated by mixing ethyl carbonate (EC) with ethylmethyl carbonate (EMC) in a 1:1 ratio for each of the measuring devices.

The time was measured from right after the impregnation of the measuringunit until the resistance value is displayed as 1.98Ω, which is theresistance value of the 0.5 M concentration electrolyte, and the resultwas shown in Table 2 below.

TABLE 2 Whether No. of Max. through-hole Through hole throughpenetration Penetration Division is formed size holes Porosity distancetime Example 1 ◯ width, length 9 36% 2 mm 0.8 sec. 6 mm Example 2 ◯width, length 9  4% 4 mm 3.4 sec. 2 mm Example 3 ◯ width, length 1 36% 6mm 7.1 sec. 18 mm Comparative X — 0  0% 15 mm   62 sec. Example 1

In Table 2, the maximum penetration distance is a value obtained bydividing the minimum length of the portion of the insulating filmcovered by the electrode plate in half. For example, in Example 1, sincethe through holes are 4 mm apart from each other, the minimum length ofthe insulating film covered by the electrode plate is 4 mm, and themaximum penetration distance divided by ½ is 2 mm. In general, theelectrolyte penetration rate is better when the maximum penetrationdistance is shorter.

Looking at the measurement results, in the case of Example 1, thepenetration time was the best result of 0.8 seconds. On the other hand,in the case of Example 2, even though there are nine through-holes as inExample 1, the penetration time was 3.4 seconds, which is significantlyslower than in Example 1 even in view of the difference in the maximumpenetration distance. In the case of Example 2, the porosity is only 4%,which seems to be because the movement of the electrolyte is inhibited.

However, in Example 3 having the same porosity as Example 1, thepenetration time was 7.1 seconds, which is slower than that of Example2. As such, it can be seen that even when having the same porosity, themore the through-holes having a uniform pattern, the better thepenetration rate.

On the contrary, it can be seen that in Comparative Example 1, in whichthe through hole is not formed, the penetration time is significantlylonger than in Examples 1 to 3.

Through the above results, it can be seen that the penetration time canbe further improved depending on the porosity and the method of formingthe through holes. At this time, it is expected that when the porosityis preferably in the range of 30 to 45%, more preferably 34 to 42%similar to the range of the insulating film of the porous material, thepenetration rate will be excellent.

In addition, when the porosity is the same, the smaller the size of thethrough hole is and the more the through holes are formed as plural, themore advantageous. However, if the size of the through hole is toosmall, the electrolyte becomes difficult to move through the throughhole, and it may be difficult to manufacture with conventionalequipment. Therefore, the horizontal cross-sectional area of eachindividual through hole is preferably 0.1% or more relative to the areaof the electrode plate. In addition, a significant increase of thepenetration effect is not expected when it exceeds 45% of the electrodeplate area. Rather, as the rigidity of the measuring unit is lowered,there is a possibility that a defect may occur during manufacturing.Therefore, it is desirable to be within 45%.

As shown in Table 2, in the case of Example 1 in which ninethrough-holes having a through-hole horizontal cross-sectional area of4% of the electrode plate area are formed, it can be seen that thepenetration rate is excellent.

EXPERIMENTAL EXAMPLE 2

On the other hand, in the measurement of the electrolyte concentrationchanges in real time, in order to verify the effect of the measuringunit according to the present invention, the following additionalexperiment was conducted.

The measuring unit of each of the above Examples and ComparativeExamples, which was sufficiently immersed in the same electrolytesolution and displayed a resistance of 1.98Ω by performing experimentalexample 1 is immersed in the electrolyte which consists of the samecomponent of 1.0M ion concentration. Then, the time taken for themeasured resistance value to be changed from 1.98Ω to 1.32Ωcorresponding to the resistance value of the 1.0M electrolyte wasmeasured, and the results are shown in Table 3 below.

TABLE 3 Whether No. of Max. through-hole Through hole throughpenetration Reaction Division is formed size holes Porosity distancetime Example 1 ◯ width, length 9 36% 2 mm 0.9 sec. 6 mm Example 2 ◯width, length 9  4% 4 mm 4.5 sec. 2 mm Example 3 ◯ width, length 1 36% 6mm 8.9 sec. 18 mm Comparative X — 0  0% 15 mm  77.3 sec.  Example 1

As shown in Table 3, in the case of Example 1, it takes only 0.9 secondsto reflect the change in the electrolyte concentration in the measuredvalue, from which it can be seen that the real-time electrolyteconcentration can be measured substantially.

DESCRIPTION OF REFERENCE NUMERALS

-   -   100: battery cell    -   110: separator    -   121: positive electrode    -   122: negative electrode    -   130: measuring unit    -   131: first electrode plate    -   132: second electrode plate    -   133: insulating film    -   140: electric wire    -   141: electric wire connected to a first electrode plate    -   142: electric wire connected to a second electrode plate

The invention claimed is:
 1. A battery cell including a measuring unit in which a first electrode plate, an insulating film and a second electrode plate are sequentially stacked, wherein the measuring unit is located between a separator and an electrode of the battery cell, and wherein the measuring unit comprises at least two wires drawn to an outside of the battery cell, wherein one of the wires is connected to the first electrode plate, and the other wire is connected to the second electrode plate.
 2. The battery cell of claim 1, wherein the first electrode plate or the second electrode plate comprises one or more through-holes.
 3. The battery cell of claim 2, wherein, when both the first electrode plate and the second electrode plate comprise the one or more through-holes, the through-holes of the first electrode plate and the second electrode plate have a same shape.
 4. The battery cell of claim 2, wherein a horizontal cross-sectional area of each through-hole corresponds to 0.1 to 45% of a horizontal cross-sectional area of the first electrode plate or the second electrode plate.
 5. The battery cell of claim 1, wherein a porosity of the first electrode plate and the second electrode plate is 30 to 45%.
 6. The battery cell of claim 1, wherein a thickness of the measuring unit is 25 to 35 μM.
 7. The battery cell of claim 1, wherein the measuring unit further comprises an additional insulating film on an outer surface of the first electrode plate or the second electrode plate in contact with the electrode.
 8. The battery cell of claim 1, wherein the first electrode plate and the second electrode plate comprise one metal or an alloy of two or more metals selected from the group consisting of aluminum, copper and nickel.
 9. The battery cell of claim 1, wherein the insulating film is comprises a material that is included in the separator of the battery cell. 